The following U.S. Patent Applications by the same first inventor, Elbert L. McKague, Jr. are being simultaneously filed and incorporated herein by reference:
U.S. Patent Application entitled xe2x80x9cApparatus And Method For Controlled Damage Of Conformable Materialsxe2x80x9d; U.S. Patent Application entitled xe2x80x9cApparatus And Method For Joining Dissimilar Materials To Form A Structural Support Memberxe2x80x9d; and U.S. Patent Application entitled xe2x80x9cComposite Structural Panel with Undulated Bodyxe2x80x9d.
1. Technical Field
The present invention relates in general to an improved structural support member, and in particular to an improved structural beam having a sinusoidal-shaped web. Still more particularly, the present invention relates to a structural support beam formed from composite materials and having a pair of end flanges joined by a sinusoidal-shaped web.
2. Description of the Prior Art
Structural support spars or I-beams typically have an xe2x80x9cIxe2x80x9d shaped cross-section with a vertically-oriented web and a crossbar or flange on each vertical end of the web. The web and flanges extend integrally down the length of the beam, but may vary in shape, thickness, etc. For example, a beam with a sinusoidal or sine wave-shaped web increases the apparent section thickness of the web. Beams with sinusoidal webs have been pursued through a variety of design and manufacturing approaches since these structures offer the potential of providing the best stiffness and strength-to-weight performance of any support structures.
Currently, all composite beams having sinusoidal webs utilize composite materials with fibers that extend continuously from the web into the flanges. The fibers are simply turned to the desired angle (90 degrees in beams having flanges that are perpendicular to the web) prior to curing resin in the beam. In essence, two xe2x80x9cCxe2x80x9d shaped sections are created and then joined back-to-back by co-curing the web area and the flange portions to outer cap laminates that laterally unite the two C-sections. Fabrication typically has involved a great deal of hand working of the composite material into the sine wave configuration. An especially labor-intensive step is required to properly turn the fibers at the corners where they transition from the curved to flat geometry between the web and flange portions of the beam. Many techniques have been used to create this configuration including lay-up and cure of previously impregnated (xe2x80x9cprepregxe2x80x9d) materials, and lay-up of dry fabric followed by resin transfer molding or other resin infusion methods. Because of the inherent manufacturing limitations of these techniques, fabric materials rather than unidirectional materials are usually required.
Achieving adequate stiffening of the web is another concern for structural spars. This problem has been addressed by increasing the composite laminate thickness of the web, or by using a flat web and attaching individual stiffening elements such as hats, blades, xe2x80x9cJ""sxe2x80x9d, or xe2x80x9cC""sxe2x80x9d. Unfortunately, these two solutions significantly increase the weight of the spar and increase the cost of fabrication, respectively. Other designs incorporate flat, stiffened, structural panels instead of sine wave webs. These latter versions typically use honeycomb cores or similar materials between the two laminate faces of a web having the appropriate planar profile. The use of such stiffened flat webs is not as weight-efficient as sine wave webs.
A structural support beam flange preform resembles the Greek letter xe2x80x9cpi,xe2x80x9d having a base with two legs extending therefrom. The preform is a composite material that is formed by weaving or braiding bundles or tows of fibers. The fibers are oriented to extend throughout each the base and legs. If used with a flat web, the preform can be woven or braided with a straight-line movement through the weaving or braiding machinery. If used with a sinusoidal web, it may be desirable to laterally deflect the axial or warp fibers back and forth to create a sinusoidal-shaped preform. Either way, the resulting preform may be either impregnated with a suitable thermoset resin, or may be unimpregnated so that resin may be infused at a later step of the overall manufacturing process.
Two of the preforms are joined to a sine wave-shaped web of the structural beam. The panel is formed from uncured, thermoset resin sheets that are reinforced with oriented fibers. The panel has two outer layers that sandwich two shorter layers on each end, and a syntactic or foamed resin layer in between. The legs of each preform straddle one edge of the panel and are shaped to both sides of the precise contours of the panel. A laminate strip is positioned against the base of each preform to create a pair of flanges for the structural support member. The assembled structure is then heated and cured. The web and/or flanges of the structure also may be configured with alternating beads, tapered in either the vertical or horizontal direction, or inclined at non-orthogonal angles. In addition, the structural support member may be formed as an I-beam, a C-beam, or a Z-beam.
The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the preferred embodiment of the present invention, taken in conjunction with the appended claims and the accompanying drawings.